The present invention relates to an eyeglass lens processing apparatus for processing the periphery of an eyeglass lens.
In an eyeglass lens processing apparatus, an eyeglass lens is held by a pair of lens chuck shafts, the lens is rotated by rotation of the lens chuck shafts, and the periphery of the lens is roughly processed by being pressed to a rough-grinding wheel. When the eyeglass lens is held by the lens chuck shafts, a cup being the fixing jig is fixed on the surface of the lens, and the lens is mounted on a cup holder of one chuck shaft via the cup, and the lens is chucked by a lens holding member of the other lens chuck shaft.
In recent years, a water-repellent lens having a water-repellent substance coated on the lens surface, to which water and oily substances are hardly adhered, has been frequently used. In the processing control that is similar to that of lenses not having any water-repellent substance coated thereon, since the surface of the water-repellent lens is slippery, the attaching position of the cup slips when a rough-grinding wheel is deeply cut in the lens, and the axial angle (that is, the rotation angle of the lens) of the lens comes off with respect to the rotation angle of the lens chuck shaft, wherein there is a problem that a so-called “axial displacement” greatly occurs.
As a method for relieving the “axial displacement,” a technique has been proposed (JP-A-2004-255561 and US2004192170), which detects load torque applied onto the lens chuck shaft, decelerates the rotation speed of a lens so that the load torque enters a range of predetermined values or the lens chuck shaft and the grinding wheel rotation shaft are moved so that the distance between the shafts is increased. Also, as another method, a technique has been proposed (JP-A-2006-334701), which rotates the lens at a constant speed, and changes the axis-to-axis distance between the lens chuck shaft and the grinding wheel rotation shaft so that the cutting depth becomes substantially constant when the lens rotates once.
However, further improvement is desired. According to the technique of JP-A-2004-255561, the load torque rapidly exceeds the tolerance of the load torque applied to the lens when the cutting depth increases, and it would be difficult to quickly decrease the torque. Further, if it is controlled that the torque is decreased by rapidly moving the lens away from the grinding wheel, there may be cases where the lens chuck shaft oscillates in the up and down directions.
On the other hand, according to the technique of JP-A-2006-334701, since there is no information regarding the lens thickness that changes due to the point of processing, if a remarkably slight cutting depth is set with safety taken into consideration so that the “axial displacement” does not occur where the thickest lens is assumed, the processing time is lengthened. If the cutting depth is constant, there may be cases where the load torque applied onto the lens chuck shaft exceeds the tolerance at a thick portion of the lens.